Disk drives are digital data storage devices which allow host computers to store and retrieve large amounts of data in a fast and efficient manner. A typical disk drive includes a plurality of magnetic recording disks which are mounted to a rotatable hub of a spindle motor and rotated at a high speed. An array of read/write heads is disposed adjacent to data storage surfaces of the disks to transfer data between the disks and a host computer. The heads can be radially positioned over the disks by a rotary actuator and a closed loop servo system, and can fly in close proximity to the surfaces of the disks upon air bearings. The heads each typically contain a separate read element and write element.
Higher data storage density on the disks may be obtained by reading and writing data on narrower tracks on the disks, and by maintaining narrower flying height gaps between the heads and the data storage surfaces. The flying height of a head can vary in response to air density changes in the disk drive, and in response to head temperature variations which can affect the distance that the tip of the head protrudes therefrom (i.e., pole tip protrusion). Writing data heats the head and can result in increased pole tip protrusion. Some disk drives controllably heat the head using a heater to vary the flying height of the head, and may temporarily decrease the heater to a low value when writing data and increase the heater to a higher value when not writing data.
Maintaining the head flying height within an acceptable range is becoming increasingly more difficult as that range is reduced to obtain higher data storage densities. Operation outside the acceptable range may result in an unacceptable read/write bit error rate and/or undesirable contact between a head and a data storage surface and potential loss of data and/or damage to the data storage surface.